ggplot 热图的反转颜色 brewer 颜色

Question

library(tidyverse)
library(RColorBrewer)
x <- LETTERS[1:20]
y <- paste0("var", seq(1, 20))
data <- expand.grid(X = x, Y = y)
data$Z <- runif(400, 0, 5)

如果我构建上面的数据框，然后用下面的代码绘制热图，我得到这个和那个：

ggplot(data, aes(X, Y, fill = Z)) + 
  geom_tile() +
  scale_fill_distiller(palette = "Reds") +                    # line 3
  # scale_fill_distiller(palette = "Reds", direction = -1) +  # line 4
  labs(x = NULL, y = NULL) +
  theme_minimal()

根据 ?scale_fill_distiller()，我认为运行 line #4 代替 line #3（上图）应该会反转我的图例的颜色：

direction argument: Sets the order of colours in the scale. If 1, the default, colours are as output by RColorBrewer::brewer.pal(). If -1, the order of colours is reversed.

本质上，热图的白色区域会变成暗红色，而热图的暗红色区域会变成白色。为什么这没有发生？运行 line #3 或 line #4 并且输出相同。

Answer 1

根据我上面的评论，让我们将两个图并排放置

gg1 <- ggplot(data, aes(X, Y, fill = Z)) +
    geom_tile() +
    scale_fill_distiller(palette = "Reds", direction = +1) +
    labs(x = NULL, y = NULL) +
    theme_minimal()

gg2 <- ggplot(data, aes(X, Y, fill = Z)) +
    geom_tile() +
    scale_fill_distiller(palette = "Reds", direction = -1) +
    labs(x = NULL, y = NULL) +
    theme_minimal()

library(gridExtra)
g <- grid.arrange(gg1, gg2)

您在上面看到的行为的原因是 scale_fill_distiller 默认假设 direction = -1：

scale_fill_distiller
#function (..., type = "seq", palette = 1, direction = -1, values = NULL,
#    space = "Lab", na.value = "grey50", guide = "colourbar",
#    aesthetics = "fill")
#{
#    type <- match.arg(type, c("seq", "div", "qual"))
#    if (type == "qual") {
#        warning("Using a discrete colour palette in a continuous scale.\n  Consider using type = \"seq\" or type = \"div\" instead",
#            call. = FALSE)
#    }
#    continuous_scale(aesthetics, "distiller", gradient_n_pal(brewer_pal(type,
#        palette, direction)(7), values, space), na.value = na.value,
#        guide = guide, ...)
#}
#<bytecode: 0x7fed742ed1d8>
#<environment: namespace:ggplot2>

ggplot 热图的反转颜色 brewer 颜色

Reverse color brewer colors of a ggplot heatmap

r

heatmap

ggplot2

colorbrewer